The present invention relates to an oscillator with a dielectric resonator and a transmitter/receiver module, which is especially useful for application to the transmitter/receiver module that uses this oscillator as the local signal generator thereof.
Traditionally, a dielectric resonator using a dielectric block with a high dielectric constant has frequently been employed as the resonator for the oscillator that operates in the high-frequency band such as the microwave or the millimeter wave. Such examples can be observed in the IEEE MTT-S 1995 International Microwave Symposium Digest, pp. 71-74, for example.
FIG. 5 illustrates an example of an oscillator using a dielectric resonator. A dielectric block 13 is placed close to a microstrip line 16 to couple the microstrip line 16 with dielectric block 13, which forms a resonator. As the dielectric block, other than the cylindrical type as illustrated in FIG. 5, a cubic type dielectric block is often used. As to an active device 15 that produces a negative resistance, a bipolar transistor is used other than the FET illustrated in the figure. The parameters of a feedback loop circuit 17 and a matching circuit 18 and the like are determined in such a manner that the active device 15 assumes the negative resistance at a desired oscillation frequency. There are various types of the feedback loop circuit, other than the one illustrated in FIG. 5.
The dimension of the dielectric block 13 is usually determined in such a manner that a resonance frequency of the lowest order mode of the dielectric resonator coincides with a desired oscillation frequency, and the resonance frequencies of the higher order modes other than the lowest order are separated as far as possible from the desired oscillation frequency. In the case of using a cylindrical dielectric block, for example, the lowest order mode is TE01δ mode, and the radius R and the thickness t of the bottom of the dielectric block is determined to meet the relation: 0.2<t/(2R)<0.4, so that the resonance frequencies of the higher order modes are sufficiently separated from the frequency of the lowest order mode.
Now, in order to realize an oscillator with a low phase noise, the Q factor of the resonator thereof should be as high as possible. The Q factor of the dielectric resonator lowers depending on the dielectric loss and the conductor loss, etc. In a super high-frequency band as the millimeter wave, the device characteristics is often insufficient in the operation frequency; and it is necessary to intensify the coupling of the dielectric block with the microstrip line and lighten the load. Here, the dielectric block is needed to sufficiently approach to the microstrip line, and since the conductor lies within point-blank range to the dielectric block, there is a possibility that the conductor loss increases and the Q factor decreases.
Also, as the resonance frequency increases, the dimension of the dielectric block decreases, accordingly the dimension in a super high-frequency band as the millimeter wave becomes extremely small. Therefore, the processing of the dielectric block becomes difficult, which results in an increase in the unit cost of the dielectric block. Further, the handling thereof becomes difficult, which increases the assembling cost of the oscillator.
To avoid such problems, there is used a method of attaining a desired frequency signal by oscillating the resonator at 1/n the frequency such as ½ or ¼ the primarily necessary frequency and multiplying the frequency of the signal by n times by using a multiplier. This method will avert the foregoing problems, because the oscillator oscillates at 1/n the frequency. However, that the operational frequency of the oscillator is 1/n the primarily necessary frequency involves enlargement of the size of the matching circuit and the like, which increases the chip size and requires a new multiplier, thus leading to cost increases due to increase of the number of chips, etc., which is disadvantageous.
As described above, the traditional system is difficult to acquire a sufficiently high Q factor in the dielectric resonator with which an oscillator for a super high-frequency band as the millimeter wave is configured, and the phase noise of the oscillator is not sufficiently suppressed, which are the problems to be solved. Further, the size shrinkage of the dielectric block accompanies difficulty of the processing, which increases the unit cost of the dielectric block. It also involves difficulty of the handling to increase the assembling cost of the oscillator, which are the disadvantages. Further, in the case of using a multiplier, the enlargement of the chip size and the increase of the number of chips result in cost increases.
It is therefore an object of the invention to solve the aforementioned problems, to restrain cost increases, and to achieve an oscillator of a low phase noise.
Another object of the invention is to solve the aforementioned problems and to configure a low cost/high performance transmitter/receiver module, by using an oscillator of a low phase noise achieved while lowering cost increases as a local signal generator for a transmitter/receiver unit.
Another object of the invention is to solve the aforementioned problems and to realize at a low cost a high performance radar system that restricts deterioration of radar performance due to phase noise, by using an oscillator of low phase noise achieved while lowering cost increases as a local signal generator for a radar system.